THE HISTORY OF EVOLUTIONARY THOUGHT 



Figure 26. Jean Baptiste La- 

 marck. ( From Locy, "Biology 

 and Its Makers," 3rd Ed., Henry 

 Holt & Co., Inc., 19.35. ) 



contemporary scientists not simply because the temper of the times was 

 opposed to evohition, for many others were skeptical of the fi.xity of spe- 

 cies, but because of the implausibility of some of his major theses. Thus, 

 his first principle, the tendency to increase in size, while it is illustrated 

 by many actual lines of descent, is far from universally true. Many groups 

 of organisms show no tendency whatever to produce strains leading to 

 gigantism. And in not a few groups, size reduction has been a prominent 

 feature of evolution. The second principle, that new organs result from 

 new needs, is quite manifestly false. In the case of plants, Lamarck be- 

 lieved that the environment acted directly upon the plant, causing the 

 production of such new characters as might adapt the plant to its en- 

 vironment. In the case of animals, Lamarck believed that the environment 

 acted through the nervous system; in other words, the desire of the animal 

 leads to the formation of new structures. In its crudest form, this would 

 mean that the man who mused "Birds can fly, so why can't I?" should have 

 sprouted wings and taken to the air. 



Lamarck did not present quite such crude examples. He did explain 

 the long neck and high shoulders of the giraffe on a similar basis, however. 

 Giraffes browse upon the leaves of trees. He presumed them to have had 

 proportions much like typical mammals originally, but as they strained to 

 reach ever higher and higher leaves, their shoulders grew higher and their 

 necks longer in response to their need. The increase was cumulative from 

 generation to generation. 



His final proposition was the inheritance of characters acquired during 

 the lifetime of the individual. This is a necessary proposition if environ- 



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